peter-h
Line Up and Wait
I am working through the wiring design for a Sandel 3500 and found some interesting issues, and wonder how people deal with these...
For example if you have a WX500 stormscope displaying on a KMD550 MFD (or any MFD) then the stormscope gets its heading from the MFD's synchro output (which in turn gets it from the HSI). The WX500 uses this to rotate the display according to the aircraft heading. So far so good. (It is somewhat bizzare that the display zoom etc are controlled by the source (the WX500) and not by the displaying instrument).
Unfortunately the display zoom and style are also set by buttons on the MFD. If one copies the WX500 data (which is RS232) to the 3500, this works but the 3500 ends up annunciating some stormscope control buttons which actually don't do anything.
And if one wires up the WX500 to be controlled by the 3500 instead, one ends up with buttons on the MFD which don't do anything.
Obviously there is a technical solution to everything, and one could have a little switch labelled "WX500 control source" which drives a relay which switches all the control signals to the WX500, to come from either the KDM550 or the 3500. A lot of wiring.... but the real fun is that that switch will have to be powered from one of the 3 buses that I have, and the KMD550 and the stormscope and the 3500 are not all powered from the same bus, so one is going to have to be quite clever where this switch+relay is energised from. One could use several diodes so that any bus can power it, but then one is not going to have an automatic fallback to an appropriate control source upon a single bus power loss.
For example if you have a WX500 stormscope displaying on a KMD550 MFD (or any MFD) then the stormscope gets its heading from the MFD's synchro output (which in turn gets it from the HSI). The WX500 uses this to rotate the display according to the aircraft heading. So far so good. (It is somewhat bizzare that the display zoom etc are controlled by the source (the WX500) and not by the displaying instrument).
Unfortunately the display zoom and style are also set by buttons on the MFD. If one copies the WX500 data (which is RS232) to the 3500, this works but the 3500 ends up annunciating some stormscope control buttons which actually don't do anything.
And if one wires up the WX500 to be controlled by the 3500 instead, one ends up with buttons on the MFD which don't do anything.
Obviously there is a technical solution to everything, and one could have a little switch labelled "WX500 control source" which drives a relay which switches all the control signals to the WX500, to come from either the KDM550 or the 3500. A lot of wiring.... but the real fun is that that switch will have to be powered from one of the 3 buses that I have, and the KMD550 and the stormscope and the 3500 are not all powered from the same bus, so one is going to have to be quite clever where this switch+relay is energised from. One could use several diodes so that any bus can power it, but then one is not going to have an automatic fallback to an appropriate control source upon a single bus power loss.